1. Field of the Invention
The present invention relates generally to media feed mechanisms and, more particularly, to a friction buckler assembly for the media feed mechanism to prevent multi-sheet feeding of recording media wherein two or more sheets are fed during a single sheet feeding operation.
2. Description of the Related Art
In a conventional single sheet printer, sheets from a media stack are indexed from the stack into the printer feedpath so as to begin a printing cycle. This operation is commonly known as sheet picking and is performed by advancing the uppermost sheet from the media stack using a motor driven roller in an arrangement sometimes referred to as a media feed mechanism which may include a rotational indexing or auto-compensating mechanism. The roller of the auto-compensating mechanism rotates against the surface of the uppermost media sheet to direct the sheet into the media feedpath for printing or other processing involving auto-document feeding.
A friction buckler assembly well known in the prior art is comprised of a friction buckler made out of a piece of ridged pellethane used to separate sheets of media as they are fed into the feed nip of an L-path printer. It is backed by a piece of foam that, along with the “legs” of the buckler, applies a spring force normal to the feed path in the opposite direction of the force applied by the media as it is fed. The amount of protrusion of the ridged rib through the buckler housing is commonly referred to as the buckler height. In order for a friction buckler to function properly, the ridged top surface of the friction buckler ridged rib must come in contact with the leading media edge and cause a buckling motion on the front of the media stack as it is put into motion by the pick tire. When the media buckles, the buckler is said to be “defeated” and the media will have a small mark on it where it has conformed to the profile of the friction buckler. Once this mark is present, the page will slide over the rest of the ridges on the top of the friction buckler surface and into the feed nip, where the rest of the printing process will occur. When media is picked by the pick tire, the media is driven down onto the friction buckler with some force (usually around 1.3 kgf) and the friction buckler assembly provides an opposite force that is slightly less than the force exerted by the media. Deflection of the ridged buckler surface occurs slightly and allows for the media to slide slightly forward until it meets a ridge and is buckled by the applied force of the pick tire. Once this buckling occurs, the media then slides over the rest of the ridges with ease and is fed into the feed nip. The crucial force to be tuned here is the backing force of the buckler assembly. This force has important implications to the feed process. As an example, a low force will allow for multiple sheets to be fed into the feed nip because of too much deflection of the pellethane buckler. Conversely, a force that is too high can cause feed problems for heavier weight medias that have higher beam strength and are more difficult to buckle.
As feed quality has become a more apparent issue due to demands for quality improvements, the ability to tune the friction buckler and the force used to buckle each sheet has grown more important. Due to the inconsistencies in the molding process of pellethane, the prior art friction buckler assembly design has varying spring forces because of the inherent physical property variations in the friction buckler, itself. Thus, a solution to tuning the spring force is to eliminate the impact of the inconsistencies of the pellethane in the system.